ISLAMABAD — Indian troops fired across the disputed Kashmir border and killed a Pakistani soldier Thursday, Pakistan's military said, in the third deadly incident in the disputed Himalayan region in recent days. Pakistan said the shooting was unprovoked, while the Indian military said its troops responded to fire from soldiers across the frontier. The tit-for-tat fighting threatens to reverse recent progress Pakistan and India have made in improving their historically antagonistic relationship. The relationship reached a recent low point in 2008 when Pakistani gunmen killed 166 people in the Indian city of Mumbai. It has improved significantly since then, and the two countries have taken steps to improve cross-border trade and ease travel restrictions. But key issues, including Kashmir, remain unresolved. A cease-fire over Kashmir has largely held for about a decade, despite periodic firing across the disputed border that sometimes causes casualties. The danger from Thursday's violence is that it comes on the heels of two more serious incidents in which Pakistan and Indian accused each other of sending troops across the border and killing soldiers, the first such accusations since the cease-fire went into effect in 2003. The Pakistani army said the latest incident occurred Thursday afternoon when Indian troops fired at a post in an area of Pakistan-held Kashmir called Battal, killing a soldier named Havildar Mohyuddin. Pakistan said the shooting was “unprovoked.” But the Indian military said its troops responded after Pakistani soldiers fired on their positions. “Our troops retaliated and an intermittent exchange of gunfire is continuing,” said Indian army spokesman Col. R.K. Palta. “It's yet another cease-fire violation by the Pakistani troops.” The most recent round of violence started Sunday, when Pakistan accused Indian troops of raiding an army post and killing one of its soldiers. India denied raiding the Pakistani post, and said Pakistani shelling had destroyed a home on its side of the frontier. — Agencies